Safety of Hydrofluoric acid vs. ammonium-bifluoride

A discussion started in
2004 but continuing through 2018

(2002)

Q. Please tell me if the relative safety of ammonium bifluoride, hydrofluoric acid and hydrochloric acid can be represented by their individual pH. I know that ABF is safer to handle than HF or HCl but I'm not sure how safe. Additionally, are there other specifics other than pH that make one chemical less dangerous to handle than the other?

Further, to put a mild etch on bathtub surfaces to make them less slippery, is one chemical better than the other. Thank you.

Michael S. [last name deleted for privacy by Editor]- Vineland, New Jersey

March 1, 2013

A. Hi Michael. The relative safety of different acids isn't easily dispatched in a forum posting, but I DO NOT AGREE that ammonium bifluoride is safer than hydrochloric acid. Fluoride ions seem to present a biohazard that most other acids don't, as they apparently can penetrate the skin and attack the bone, and some people have reported an anesthetic effect such that a burn can go undetected until it is very severe. People have died from hydrofluoric acid burns, and I'm not sure whether that is the case with hydrochloric acid.

I'd say the general rule should be never use fluoride chemistry unless indispensable but, if you must, then ammonium bifluoride can be somewhat safer to have around and can perhaps be used more safely than hydrofluoric acid because its concentration is more limited.

As for etching a bathtub, remember that some are fiberglass, others acrylic, or porcelain, or cultured marble; acid will react with them all differently. Further, the acid splash and even the acid fumes will attack any metal in the drains, faucets, or elsewhere in the bathroom. Both from a personal safety viewpoint and a potential damage viewpoint, I wouldn't do it. Please either retain a professional bathtub surfacing company whose employees have received haz-mat training, or make do with a non-slip mat. Good luck.

Regards,

Ted Mooney, P.E.finishing.comPine Beach, New Jersey

Ammonium bifluoride for etching glass?

2001

Q. We are currently using hydrofluoric acid to etch glass, but have heard that ammonium-bifluoride may be safer. Is anyone aware of its performance compared to HF? And since it is in powder form, is it safer?

Thanks,

Robert Gauthier- Danbury, Connecticut, USA

2001

A. Ammonium Bifluoride, NH4HF2, is a weak acid salt of HF. If you add Sulfuric or Hydrochloric acid to the ABF you will have more HF in solution than with just the ABF. You will have to do some chemistry to figure the molar amount of acid needed to get the equivalent amount.

George ShahinAtotech - Rock Hill, South Carolina

2001

A. Hi,

I have used both ABF and HF a lot and know from first hand experience the effects of 70% acid on finger tips (A hole in glove). I have never had a burn with solid ABF, however (breaking lumps with bare hands). It does hurt when it gets in a cut or scratch but a quick rinse with water helps. This said, you should always wear eye and skin protection when mixing or using, and never handle ABF with your bare hands.

James Chunn- Theodore, Alabama

2004

A. Even though they both produce a corrosive fluoride solution, ABF and HF are quite different.
HF is water-soluble in all proportions while ABF is soluble only up to ~28% at room temperature. ABF, in solution, yields ~ 1/3 as HF and ~2/3 as ammonium fluoride(AF) and, as such, provides a somewhat buffered solution (a 28% solution of ABF). In fact, semiconductor-chip manufacturers use different ratios of HF and ABF to produce various "Buffered Oxide Etches" that dissolve silica chips at various rates.

The use of (dry) ammonium bifluoride as a "safe" replacement for hydrofluoric acid is an unsafe practice. The uninitiated person who judges this as "safe" can quickly get into trouble since once the ammonium bifluoride (NH4F)HF is contacted with water; the HF content will be ~ 13% ... very corrosive, toxic and hazardous.

Some folks have used ammonium bifluoride as a substitute for HF and created (what they refer to as) an "acid free" wheel cleaner -- it's a dangerous and deceptive practice.

Bottom line here is that the ABF solution will still produce an extremely hazardous liquid.

Mike Berg- St Louis, Missouri, USA

(2007)

Q. We also use a combination of ammonium bifluoride, caster sugar and distilled water to etch glass. Does anyone have knowledge as to whether the addition of the caster sugar, and the distilled water, would make this combination more, less or equally hazardous?

Laurie Mills- Kallaroo, Western Australia, Australia

January 23, 2011

Q. What is the function of the caster sugar ?

Moshe A - Israel

June 22, 2011

A. The function of sugar is make it less liquid. It is easier then to apply (honey consistency).

David Karafiát - Krupka, Czech

July 15, 2013

Q. I read a comment from Laurie Mills of Western Australia. Where can I purchase Ammonium Biflouride in Victoria? Any help would be appreciated .
Laurie

Laurie Mattila - Melbourne, Victoria, Australia

July 15, 2013

A. Hi Laurie. This is an industrial chemical that won't be found in a supermarket, but depending on volume and purity required I'm sure it's offered by both "laboratory supply" services and "commodity chemical" companies. And glass etching creams which contain ABF, and possibly HF, are widely available. Please explain your situation and additional help may be available. Good luck.

Q. I am trying to etch thick glass bottles. I'm using ammonium bifluoride and sulfuric acid in a water bath. My mix is 1 Kilo of ammonium bifluoride, 2 liters of sulfuric acid, in 3 gallons of water. I know I'm close but no luck yet. Any help would be appreciated.

I use ABF to etch glass bulbs. About 5 Kg of ABF crystals is dissolved in 110 litres of DM water. I see white patches on the bulbs after etching, can anyone suggest how to get rid of white patches.

Sharmila B H- INDIA

April 25, 2012

Q. I mixed ammonium bifluoride, barium sulfate, caster sugar and distilled water to make etching cream. I find it effective, however, continuous bubbles form in the solution, I wonder why. Can somebody help me explain. What must I do to prevent bubbles from forming continuously. Thanks.-Carlos

Carlos Espinoglass etching - Walnut, PHILIPPINES

Are ABF and HF interchangeable?

2004 -- this entry appended to this thread by editor in lieu of spawning a duplicative thread

Q. I'm working in a consulting company in Russia with a project about a chemical factory. Our client was producing hydrofluoric acid and is now thinking about replacing this production with production of ammonium bifluoride. In this case it is not a matter of safety, but they think that it is easier for transportation, storage and use because ABF is dry. What do you think about this?

And another question. I wonder is ABF and HF are totally interchangeable or they have some different characteristics?

Victoria Kiryakova Alt - Saint-Petersburg, Leningradsky, Russia

2004

A. They are not totally interchangeable. It is common to use ABF in an acid solution as a source of fluoride ions. It will work very nicely on many, but not all applications.

James Watts- Navarre, Florida

----Ed. note: We have many threads on line here regarding those specific applications. Please try the search engine, adding terms related to the different potential applications like "aluminum", "stainless steel", "glass", etc.

Making an aluminum brightener

April 12, 2012

Q. As I read your thread above, it appeared you were indicating for an aluminum brightener use 28% (wt) ammonium bifluoride to 72% (wt) water. Is this correct or is this a concentrated ratio that should be cut? Do you recommend any other additives? Does adding Ammonium bifluoride to water create a violent reaction heat, fumes, etc.?

George Rodgers- Charleston, South Carolina, USA

April 14, 2012

A. Hi, George. Mike was saying the solubility of ABF is 28%. I'm quite sure he wasn't suggesting a formulation for an aluminum brightener, which might include many different ingredients and additives; I think he was just explaining areas of equivalence and non-equivalence between HF and ABF.

What exactly are you trying to do? ABF is dangerous; if you don't know about its reaction heat, fumes, etc., are you sure you have received the necessary haz-mat training? Thanks.

Regards,

Ted Mooney, P.E.finishing.comPine Beach, New Jersey

April 16, 2012

Q. Looking for a formulation of an aluminum brightener for the auto/marine industries that I can use to clean (brighten the aluminum) of car wheels covered in brake dust, tractor trailers, pontoons on boats, etc. Usually this is sprayed on with a spray bottle of brushed on with a wash brush. Thanks, George.

George Rodgers - Charleston

April 17, 2012

A. Hi again, George. One reason I asked is that fluorides are very hazardous, so it is imperative that proper protective equipment including goggles and gloves be worn. The cleaner would probably have some other ingredients like a mild abrasive like feldspar and perhaps a wetting agent like sodium lauryl sulphate. If you are a consumer, there are number of companies already offering this product commercially, and you should use a packaged solution rather than attempt to custom formulate from raw chemicals.

If you are a manufacturer intending to market a fluoride-based cleaner like this, I think your plan must first be examined by a knowledgable consultant ... you can't possibly market such a product without your company intimately understanding the chemistry. Plus, you need to carefully study patents and do reverse engineering, or you'll be starting from zero 50 years behind your competitors :-)

Good luck.

Regards,

Ted Mooney, P.E.finishing.comPine Beach, New Jersey

March 4, 2013

A. Hi All, Looking through the responses to this letter and the amounts people are using made me wonder if the solutions being suggested are of the right percentage.
The percentage of ammonium bifluoride in a solution should be no more than 20 %. this equates to 20 g to every 100 mls water.

That 20% solution is the MAXIMUM amount found in proprietary brands and "home brewers" should start with lesser amounts finding what works for them.

I would be interested in hearing how previous responders have gotten on with the solutions they have posted here in the last couple of years.

Anthony BennettSandblasting - South West U.K

Calculations for ammonium bifluoride

(2007)

Q. Is there any way to calculate the concentration of the ABF flakes when combined with water?

Philip Rossi electronic glass - Vineland, New Jersey

January 14, 2013

Q. Can someone tell me the right percentage mixture of ammonium bifluoride, water and oxalic acid that will keep the pH of the solution between 2 and 3?

Rick Law - Philadelphia, Pennsylvania

December 12, 2013

Q. I've been out of college too long to remember my stoichiometry. If I need a 5% solution of a hydrofluoric acid solution but would rather use ammonium bifluoride, how much do I use?

Jolene Dramson - Hartford, Connecticut

January 14, 2014

A.
Ammonium bifluoride has a molecular weight of 57.0432 and hydrogen fluoride (HF) has a molecular weight of 20.006. Ammonium bifluoride can be viewed as a mixture of ammonium fluoride and hydrogen fluoride. Ammonium bifluoride is therefore 35.072% HF. So if you desire a solution that contains 5% hydrogen fluoride you need 2.85 times as much or 14.25% ammonium bifluoride. If you desire a solution that contains HF equivalent to 5% of the commercial product (typically, but not always, 48% HF) you will want 48% of this or 6.84% ammonium bifluoride. However, the ammonium fluoride will have a buffering effect on the solution and solutions prepared as described above will not be as active as their HF concentration would indicate. The desired strength will have to be determined experimentally. These calculations, though, will give you an idea of where to start your experiments.

!! I'm a little startled to see so many questions and answers about the use of HF and ABF without reference to the proper safety precautions when using either of these hazardous chemicals.

While ABF is in one sense safer to use, since it is less likely to be splashed (like liquid HF) as it is in a solid form, its use still requires the same precautions you would take when working with HF or solutions thereof because solid ABF readily absorbs moisture which in turn forms a solution of concentrated HF. To give an example, crystals of ABF that were left next to a balance (ahem, after a prior user did not properly clean up after themselves) though dry, absorbed enough moisture from the air to etch away the lab bench top surface, leaving permanent white spots on the black laboratory grade benchtop material.

In both cases, whether HF acid or solutions thereof, or ABF or solutions thereof (which contain HF), double gloves that are compatible with HF acid should be used. Work should be performed in a properly ventilated area, preferably in a chemical fume hood. Working in a bathtub for example with the bathroom vent on does not equate to a safe working environment. Etching with these chemicals should be done in a chemical fume hood. Proper PPE including safety glasses and protective garments are a must.

Calcium gluconate gel should be on hand at all times. HF burns to the skin must be treated immediately by flushing with water and applying calcium gluconate gel followed by immediate medical attention by a trained professional. This includes any sort of contact of ABF in the solid form as HF is formed when moisture in your skin combines with the solid ABF. If you haven't received training on how to properly treat HF burns don't use these chemicals.

This is not the sort of burn where you simply wash it off and go about your business. While you are performing the initial flush with water have someone else contact 911 immediately.

As noted, when ABF comes in contact with water, HF is produced. HF burns on the skin penetrate very quickly and often do not have the same pain associated with a burn from nitric or hydrochloric acid. This is deceptive as the HF can penetrate without causing significant pain but the resulting damage from an HF burn can be more dangerous due to the nature of the fluoride ion.

This wikihow article provides a good overview of the dangers and treatment for HF burns. I would ignore the part about using other treatments - if you don't have Calcium Glucunate gel on hand DO NOT USE HF or ABF or any other chemical that poses the risk of an HF burn! Reading this article or my post does not constitute having received training for treatment of HF burns in my opinion.

http://www.wikihow.com/Treat-a-Hydrofluoric-Acid-Burn

My advice - do not use these chemicals unless you have received specific training in their safe handling and use. As someone who has received such training, and has used these chemicals in a laboratory setting with proper PPE and ventilation controls, I would never consider using them in a household application.

Stay safe!

David Beck - Lancaster, Pennsylvania, USA

----Ed. note: Thank you for the excellent, highly detailed response, David! But there were no less than four previous postings about the extreme dangers of HF and ABF just on this one page, including warnings not to use them without specific training.

August 4, 2016

A. I read your many questions and answers page, but I think two chemicals use another solution. I have a business of glass etching near about 7 to 8 years. I use HF and ABF another -- another solution for 2 another glass etching, ABF with solution use for frosting design and HF solution.

For deep etching, when necessary of chemical etching on glass, when necessary of deep etching, I use another way: sand blasting for frosted and also deep etching process. Nowadays, I think chemical etching is hazardous so, can we use blasting process? It is better for tomorrow, for own safety.

Sanjay Datta - Serampore, West-Bengal, India.

May 11, 2017

A. To complete David Beck's answer, which gives by far the best and safest advice --

One should do such work under chemical fume hood dedicated for work with fluoric acid. They're made from plastic only, and the ventilation is equipped with a water trap. Otherwise, vapors will corrode the ventilation system, and it can be pretty bad in case of extensive use.

Jebril HADI - Bern, Switzerland

December 19, 2017

Q. Chimex LTD. has on their website some mixtures of etching (matting) solutions. I am particularly interested in their mixture of 75 grams of Ammonium Bi-fluoride, 75 grams Barium Sulfate and 100 ml of water. My question is:
Is this an aggressive mixture and if so can it be buffered by adding more Barium Sulfate? Thanks.

Jon Wilson - lexington, Massachusetts USA

Glass etching cream is not strong enough

July 1, 2018

Q. I use an easily available etching cream to etch glass but I find that the paste mix is not strong enough and does not give the milky white finish that I require. I have access to 98% strength sulphuric acid, would adding more acid make the mix stronger. Or does anybody have any other ideas. I believe that the current paste mix for 30 grams of paste is:
6 grams barium sulphate. 3.3 ml sulfuric acid. 2.5 grams sodium bifluoride. 1.5 grams ammonium bifluoride.

A. Hi Myrick. Wikipedia explains how it can be done, but calls it "a once contemplated route" rather than a practical process. Simply mixing other chemicals with ABF will not convert it into HF, but some F - ions will be present in a solution of ABF.

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.